模块化

“格式化”字符串

“%s %e”  %   ("Value is", 16.0 ** 0.5)       显示一个字符串，后面跟着4.000000e+00。

"%7"   %   (11232/3)       显示计算结果，并用空格填充。

"%X"    %   127       用16进制显示数字。

"%20s "    %    "Banana swirl"       把字符串填充到20位长，然后显示一个换行字符。   意味着换行。

"%s is $%4.2f"      %  (“Popsicle”, 1.754)      和字符串一样，显示一个2位十进制的浮点数。（16进制数会用来表示网页颜色之类的东西。）

“%s %f”  %   ("Value is",16.0 ** 0.5)     显示一个字符串，后面跟着4.000000。

“%07d”    %  (11232/3)      显示用0填充的值。    %后面的0意味着“用0填充”。

一个简单的pos程序：

def save_transaction(price,credit_card,description):
    file=open("transactions.txt", "a")
    file.write("%16s%07d%s
" % (credit_card, price * 100, description))
    file.close()


items=["DONUT","LATTE","FILTER","MUFFIN"]
prices=[1.50,2.0,1.80,1.20]
running=True


while running:
    option=1
    for choice in items:
        print(str(option)+"."+choice)
        option=option+1
    print(str(option)+".Quit")
    choice=int(input("Choose an option:"))
    if choice==option:
        running=False
    else:
        credit_card=input("Credit card number:")
        save_transaction(prices[choice-1],credit_card,items[choice-1])
        

运行结果：

Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:43:06) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option:2
Credit card number:63827462387648620000220
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option:3
Credit card number:63827462387648320000180
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option:5
>>> 

　　进行模块化：

from transactions import *

items=["WORKOUT","WEIGHTS","BIKES"]
prices=[35.0,10.0,8.0]
running=True


while running:
    option=1
    for choice in items:
        print(str(option)+"."+choice)
        option=option+1
    print(str(option)+".Quit")
    choice=int(input("Choose an option:"))
    if choice==option:
        running=False
    else:
        credit_card=input("Credit card number:")
        save_transaction(prices[choice-1],credit_card,items[choice-1])
        

　　

from transactions import *

items=["DONUT","LATTE","FILTER","MUFFIN"]
prices=[1.50,2.0,1.80,1.20]
running=True


while running:
    option=1
    for choice in items:
        print(str(option)+"."+choice)
        option=option+1
    print(str(option)+".Quit")
    choice=int(input("Choose an option:"))
    if choice==option:
        running=False
    else:
        credit_card=input("Credit card number:")
        save_transaction(prices[choice-1],credit_card,items[choice-1])
        

　　两个程序共用的程序（模块）

def save_transaction(price,credit_card,description):
    file=open("transactions.txt", "a")
    file.write("%07d%16s%16s
" % ( price * 100, credit_card, description))
    file.close()

　两个程序运行的结果：

Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:43:06) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option:1
Credit card number:6432425412474321
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option:5
>>> ================================ RESTART ================================
>>> 
1.WORKOUT
2.WEIGHTS
3.BIKES
4.Quit
Choose an option:1
Credit card number:7649463856424326
1.WORKOUT
2.WEIGHTS
3.BIKES
4.Quit
Choose an option:4
>>> 

价格下降了两次进行打折：

from transactions import *
import promotion
import starbuzz1

items=["DONUT","LATTE","FILTER","MUFFIN"]
prices=[1.50,2.0,1.80,1.20]
running=True


while running:
    option=1
    for choice in items:
        print(str(option)+"."+choice)
        option=option+1
    print(str(option)+".Quit")
    choice=int(input("Choose an option:"))
    if choice==option:
        running=False
    else:
        credit_card=input("Credit card number:")
        price=promotion.discount(prices[choice-1])
        if input("Starbuzz card")=="Y":
            price=starbuzz1.discount(price)
        save_transaction(price,credit_card,items[choice-1])
        

　　打9折：

def discount(price):
    return 0.9*price

　　打95折：

def discount(price):
    return 0.95*price

　　

运行结果：

Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:43:06) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option:4
Credit card number:5413765853576543
Starbuzz cardN
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option:2
Credit card number:5413765853576543
Starbuzz cardY
1.DONUT
2.LATTE
3.FILTER
4.MUFFIN
5.Quit
Choose an option: